Room area calculator
Calculate room area for a rectangle, an L-shape or a room with a void. A boundary that crosses itself shows an error, not a number.
Worked examples
Each control loads that case on the sheet. The figures are the ones the scale, the outline, or the waste setting produces. They are not sample captions pasted over a different result.
Skirting, paint and the auto-dimension sheet use a traced floor plan. Open the takeoff desk when the boundary is the one you mean to order against.
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Results depend on drawing quality, the calibration length, and where you trace. They are not a substitute for measuring on site, a statutory valuation, or a professional quantity survey.
How the numbers are produced
This page checks one outline. It does not open Elm Cottage. The sheet draws the shape you pick, with no dimension text on the drawing, and the readout is the shoelace area of the vertices you see in the table below. The first shape is a rectangle 4.00 m by 3.00 m. Area is 12.00 m². Perimeter is 14.00 m, two lengths and two widths: 4 + 3 + 4 + 3. The vertices are (0, 0), (4, 0), (4, 3), and (0, 3). Units are metres. No scale factor is applied, because these coordinates are already real.
The metric L is a 4.00 m by 3.00 m rectangle with a 1.00 m by 1.00 m notch taken from one corner. Vertices run (0, 0), (4, 0), (4, 2), (3, 2), (3, 3), (0, 3). The outline is concave and it does not cross itself. Area is 12.00 m² minus 1.00 m², which is 11.00 m². Perimeter is 14.00 m. The notch adds two edges and removes one, and the lengths still sum to 14.00 m. A concave corner is allowed. You trace every turn in order.
The foot L is 20 ft by 15 ft with a 5 ft by 5 ft notch. Vertices are (0, 0), (20, 0), (20, 10), (15, 10), (15, 15), and (0, 15). Gross rectangle would be 300.00 ft². The notch is 25.00 ft². Net area is 275.00 ft². Perimeter is 70.00 ft. The unit is feet because the coordinates are in feet, not because a metre plan was converted. 275.00 ft² is not a conversion of the 11.00 m² L. They are different rooms.
A void is a second outline inside the first. The outer rectangle is again 4.00 m by 3.00 m, 12.00 m². The void is (3, 2), (4, 2), (4, 3), (3, 3), which is 1.00 m by 1.00 m, 1.00 m². Net area is 11.00 m². Gross and deducted are shown only for this shape. The shared edge of the void with the outer corner is not treated as a crossing. A void that cuts across the outer boundary is a real intersection and is refused. Use a void for a stair opening or a chimney breast you do not want in the floor area. Do not draw the void as a separate room and then subtract it by hand.
The bowtie is (0, 0), (2, 2), (0, 2), (2, 0). The edges cross. The area is hidden and the message says the outline crosses itself. There is no number to copy. Fewer than three corners is the other refusal: an outline needs at least 3 corners. Move a vertex until the edges no longer cross and the area returns. The tool will not pick the larger triangle and call that the room.
Which line you trace is the whole measurement. The inside face, the centreline, and the outside face of the same wall are different polygons. A 4.00 m by 3.00 m inside face is 12.00 m². Moving each wall out by 0.10 m makes a 4.20 m by 3.20 m face, which is 13.44 m², about 12 percent more. Compare rooms on the same face. This page does not choose the face for you. When the outline is the one you mean, the takeoff desk can turn it into floor, skirting, and paint. The scale of a scanned plan is a different job: calibrate on the measure page, then trace.
Where these figures get used
A rectangle room quoted as 4 by 3 metres is the first button: 12.00 m² and a 14.00 m perimeter. If your notes say 4.00 by 3.00 and the button disagrees, the notes are not a simple rectangle. Step through the L before you invent a second room.
An L-shaped lounge with a 1.00 m return is the metric L: 11.00 m², perimeter still 14.00 m. The 20 ft by 15 ft lounge with a 5 ft return is the foot button: 275.00 ft² and 70.00 ft. Keep the unit with the coordinates. Do not feed foot numbers into the metre shape and multiply by 0.3048 afterwards; the foot shape already reports feet.
A stair hole of 1.00 m² in a 12.00 m² room is the void button: gross 12.00 m², deducted 1.00 m², net 11.00 m². If the hole outline crosses the room, you get the bowtie error instead of a negative area. The floor plan dimensions page is where offset leaders are explained; this page only decides whether the boundary is a valid polygon.
Offset leaders, the 40 mm scale table, and the 1.92 m versus 2.00 m gap are drawn on the floor plan dimensions page.
Common questions
How do I measure an L-shaped room?
Trace every corner in order. The worked L is 4.00 m by 3.00 m with a 1.00 m by 1.00 m notch, which is 11.00 m². A 20 ft by 15 ft room with a 5 ft by 5 ft notch is 275.00 ft².
How do I deduct a stair or a chimney?
Draw the room outline, then draw the opening inside it. The floor area is the outer area minus the void. The void in the worked example is 1.00 m², so a 12.00 m² rectangle becomes 11.00 m².
Why is there no area?
The outline crosses itself, or it has fewer than three corners. Move a corner until the outline no longer crosses. The tool will not guess an area.
Which line should I trace?
Trace the face you intend to measure, and use that same face for every room you compare. A different face changes the area.
The rest of the desk
Each of these opens the same measuring rules on a different job. Calibration is shared. A scale you set on one page is not stored for the next visit.